Basic How to: Synchronize Orbit

[Divinux]

Hi guys,

for my first post i wanted to show what i learned so far about orbiting, and maybe help those out who come across this wondeful game after me. I noticed this section was lacking an easy visual guide to what i struggled with for quite a bit, so here goes my attempt at it. I will try to describe operations which will help you controlling your orbit, and as an example synchronize my orbit with the Mun\'s. Of course, mastering these operations will help you land on whatever planet you want in the future.

So, let\'s start with some theory:

Every orbit has two critical points, an Apoapsis (the point farthest away from the center of gravity) and a Periapsis (the point closest to the center of gravity). You should watch out for them because they make modifying your orbit easier and also tell you something about your speed and height. On your way to the Apoapsis you will be trading height for speed, and on your way to the Periapsis you will be gaining speed, but losing height.

Ok, enough theory for now, we will figure the rest out as we go

Off to the launchpad!

Step 1: Achieving lower orbit

Well, let\'s hope this ends well : Last preflight checks, enable the S.A.S.(Hotkey T) and liftoff in 10...

Start rising vertically until you leave the atmospere. If you open the map(Hotkey M), you should already see your trajectory and an Apoapsis. It should look something like this:

Remember, the Apoapsis being the highest point, is the point where you start falling if you proceed without any more thrust, so you can either raise it more, or if it\'s high enough for your taste, cut your engines (Hotkey X) and take your time to reposition the rocket. You will want to translate your vertical velocity into horizontal, so you should line up your ship with the horizon. The Mun\'s orbit has an inclination of 90°, so it being our ultimate goal, i suggest you turn there.

91°.. Mhh almost but good enough for now. Start accelerating and watch your orbit grow bigger until the Periapsis appears. Welcome to lower orbit! Now, is your orbit not perfectly circular? We can fix that! For the orbit to be a perfect circle, you will need the Periapsis to be the same height as the Apoapsis. To modify a point, you need to be on the opposite side, so to modify the Periapsis, wait until you reach the Apoapsis and vice versa.

As you might know from the tutorial, the green marks on your instruments indicate where you go and where you come from. Point your rocket at them to accelerate (burn prograde) or 'brake' (burn retrograde). Tinker with it as much as you like and you will get something similar to this:

Step 2: Aligning orbital planes

Now that we have a nice stable little orbit going on, we can start worrying about our orbital plane. Basically, you can imagine your and the Mun\'s orbits as CDs and we have to make sure we align them parallel to each other, so we don\'t miss the Mun later. You might have done a better job, but since i was heading at a course of 91° from the beginning, my plane is a little off.

To fix this, i will have to rotate my plane, and the best point to do this is on the axis between the two orbits.

Basically, you will need to accelerate at 90° in the direction you want the plane to rotate.

Note that you don\'t see the green orbit indicators on the instruments. This is because you need to position your rocket at a 90° angle up or down and the indicators are exactly on top and bottom of the ball now. The green arrows indicate my course. In the special case of our 90° inclination, you just need to position your rocket north at HDG 000 to rotate your orbit counterclockwise, or at HDG 180 to rotate it clockwise.

In any other case it helps to point your rocket in your orbit\'s direction, rotate your rocket so the ground/air indicator is vertical (i did a better job on the bottom right), and then rotate the rocket 90° on the horizon line in the direction you want your orbit to rotate.

It takes a bit to wrap your head around, to process where 'up' is and where you should go, but once you did this, the reward will be a perfectly aligned orbit.

Step 3: Transferring into higher orbit

Great, now that we have a stable and aligned orbit, we will be transferring to the Mun\'s orbit. This step should be easy now, all we have to do is to burn prograde at the Periapsis, so the Apoapsis moves to a height of about 11.000.000m.

Once we have that, we wait until we reach the Apoapsis and burn prograde again until the Periapsis hits 11.000.000m as well.

Step 4: Synchronizing both orbits

Now that we are almost in the same orbit as the Mun, it should become painfully obvious how far away from it we are. All we have to do to 'hunt it down' is to alter our orbit just a tiny bit- a smaller orbit takes less time for a full rotation than a bigger one. We can make our orbit just a tiny bit smaller in radius to catch up with the Mun, or make a bigger radius to let the Mun catch up with us. As you can see, the Mun was slightly in front of me, so i decided to catch up from behind.

All it takes now is a few orbital periods in fast forward... Until eventually...

You get captured by the Mun! Congratulations!

Now you can safely make it back using the very same methods, or, if you have a landing pod prepared, land on the Mun!

[deadshot462]

Great guide.

This will be very useful for people trying to catch up to satellites and space stations.

The difficult part is aligning orbit planes due to lack of orbit inclination indicator atm, but I\'m sure people will still manage just fine with the bigger challenge.

[PD]

Welcome to the KSP Forums! And what a way to get involved!! - Great and detailed guide!

PD

[Huojin]

Great guide.

This will be very useful for people trying to catch up to satellites and space stations.

The difficult part is aligning orbit planes due to lack of orbit inclination indicator atm, but I\'m sure people will still manage just fine with the bigger challenge.

This is exactly what I was thinking about during this. Very useful. And I think it\'s helped my comprehension of the orbital plane issue.

[witeken]

Awesome! This should be sticky.

Bit I have 2 (or 3) little comments.

You should have said something about the atmosphere. Some newbies might not know that you cannot arbit in the atmosphere. Secondly, You also should have said that if you want to get a low orbit from the start, you can warp time till you\'re at apoapsis and burn there to orbit.

And one very small last thing. If you want to make it completely newbie friendly, you should have add a craft to it.

edit: Welcome to the forums! Fantastic first post

[madmat]

That was an awesome read. Now it\'s starting to make more sense,,page saved for further consultation,,,cheers again,,

[Uri G]

Excellent first post and tutorial,well done and welcome to the forum! Would be good to see that on a you tube type tutorial. Great job 8)

[kevinlacht]

Very good post, only one question: How you make your orbit rounder?

[witeken]

Very good post, only one question: How you make your orbit rounder?

You go to the highest apsis and there you increase your speed. He said it in the tut. If you increase/decrease speed at lowest apsis, the altitude at highest apsis will get higher/lower and vice versa.

[kevinlacht]

But wich way, to the purple or the yellow dot ore what?

You go to the highest apsis and there you increase your speed. He said it in the tut. If you increase/decrease speed at lowest apsis, the altitude at highest apsis will get higher/lower and vice versa.

[Corax]

But wich way, to the purple or the yellow dot ore what?

[Volt]

Great guide, thanks a lot, but I have one question: How do you find the point at which the two orbits intersect? As in the diagram of the two green orbits?

[Divinux]

Hi guys,

and thanks for the welcoming words!

Great guide, thanks a lot, but I have one question: How do you find the point at which the two orbits intersect? As in the diagram of the two green orbits?

Unfortunately, there is currently no indicator for plane alignment. As long as we\'re in the stoneage, instrumentwise, we(at least me, let me know if there\'s a better way) do it by eye. I open the map, scroll out until i see the front- and the backline of the Mun\'s orbit, rotate up or down until both lines are lined up into one, and then rotate right/left until the intersection is about in the middle. I must admit i fly this maneuver in map view completely to see where my rocket is relative to the intersection.

But wich way, to the purple or the yellow dot ore what?

Check out the picture Corax linked. As you can see, there are two yellow dots (they look limegreen to me ) The one labeled prograde is 'forward' the one labeled retrograde is 'brake'. So assuming you are on the green orbit, you need to burn 'forward' to make your orbit bigger(like the blue one), or 'brake' if you want your orbit to shrink (like the red one). It\'s all colorcoded

Excellent first post and tutorial,well done and welcome to the forum! Would be good to see that on a you tube type tutorial. Great job 8)

Thank you Sir! There are several videos on youtube about that, and i learned a lot from Lets plays actually. So i dont think i could contribute very much because of the existing content. Maybe when the instruments get updated

[...]Bit I have 2 (or 3) little comments.

You should have said something about the atmosphere. Some newbies might not know that you cannot arbit in the atmosphere. Secondly, You also should have said that if you want to get a low orbit from the start, you can warp time till you\'re at apoapsis and burn there to orbit.

And one very small last thing. If you want to make it completely newbie friendly, you should have add a craft to it. [...]

I did say literally one word about the atmosphere, and to modify the orbit at the apoapsis or periapsis i mentioned as well, i might have to make it more clear then I wanted to edit the post anyways, and add your information as well as what PD sent me via PM.

About the craft, i don\'t want to add the one i used, because there are as you can clearly see mods involved, and i can\'t imagine that going too well I might throw a vanilla rocket capable of reaching Mun\'s orbit together though... About the same time as the youtube video ;D

[SynMonger]

On the subject of plane change, I set up a few screen shots to supplement the ones by Divinux:

Prograde:

Increase apoapsis and periapsis altitude

Retrograde:

Decrease apoapsis and periapsis altitude

Orbit Normal +:

Increase inclination at ascending node

Decrease inclination at descending node

Orbit Normal -:

Increase inclination at ascending node

Decrease inclination at descending node

Edit: fixed a few typos. Also, if anyone wants to use these screen shots, feel free.

[Dynamo]

Wow. I\'ve been waiting for something like this. This is almost everything about orbit correction, which i am REALLY bad at.

Thanks a lot.

[michealv]

I\'ve heard that the syncing orbits can be applied when you want to craft in space to meet up with each other, i\'ll use an example that I\'m struggling with.

Ship A wants to intercept Ship B, Ship A is on a lower orbit than Ship B to try to catch up to it.

Ship A eventually lines up with Ship B at around 10km orbit, however Ship B it orbiting at 16km.

How do I get Ship A to jump up to Ship B altitude, without wrecking the orbit on the other side of the planet (in this case the mun).

I have thought about (not yet tested) using RCS boosters to get me to the right altitude, could this work?

List of things tried

1.) Upon catching up with the target craft, make the Apogee and Peri the same as the target ship (Failed)

2.) Attempt to use RCS to increase/decrease the crafts altitude to intercept (Failed)

3.) Attempt to \'anticipate\' when the crafts will intercept and match at least their Apogee or Peri at interception to be at the same location (Failed)

4.) Followed the purple marker once both ships were close (Insta fail, its just points to/away from kerbin even within 5km of the craft)

5.) Thrusting upwards/downwards using the engines, keeping the bar on perfect vertical as to not increase/decrease horizontal speed (Failed)

6.) Following the diagram on the Orbit calculator (well dont even understand it so fail)

Edit Ok I\'m still trying, I\'ve used the KSP Orbit Mechanic & do not understand how to use it to intercept my other ship. I\'m not asking for someone to hold my hand but please, if anyone can at least guide me in the right direction I should be able to go from there.

Solved! - I\'d like to thank Trydyingtolive for his awesome video on how to do this (found here

). Your my hero lol - the trick is to let the craft catch up by whatever means (higher ap or lower per than the target) and then when it caught up slowly fix both per and ap to match both crafts, in my case this was 50,000m. From there I used two tanks of RCS fuel to carefully jettison myself towards my target

[WX_Echo]

Edit Ok I\'m still trying, I\'ve used the KSP Orbit Mechanic & do not understand how to use it to intercept my other ship. I\'m not asking for someone to hold my hand but please, if anyone can at least guide me in the right direction I should be able to go from there.

Although it appears you\'ve found an operational solution to your problem, the theoretical tools to solve the standard intercept condition are available in my Java calculator.

This example assumes a simple intercept scenario in which the target object (could be a celestial body or a spacecraft) is orbiting in a circular orbit at a larger orbital altitude than your spacecraft (which is assumed to also be in a circular orbit). For the image I assumed your spacecraft is in a parking orbit of 150 km around Kerbin and the target craft is at 500 km. If the two objects are in opposition at time zero (you could use the actual game time of your situation as well), then you should burn at time 01:13:21 (HH:MM:SS); this will provide you with the intercept angle needed to intercept the target. All of the actual Delta-V data (first and second burn values) are provided as well.

Hope this helps!

FYI - It is my intent to include support for orbit phasing in my next update.

[michealv]

Thanks for that, that simple explanation helped me to understand the key areas of your tool to help me achieve future interceptions.

As you can probably see, I had a very hard time with this, and in the end I had to find the answer off of the forums which I found a tad disappointing.

I hope my comments on this thread helps others who are trying these sorts of things for the first time in Kerbal, have a more pleasant experience than what I initial did.

Keep up the good work on the calculator!

Edit: on a side note, do I need to worry about the delta V that my engines can produce? (nvm at that orbit almost anything would work lol)

[illectro]

This is my video tutorial on orbital rendezvous - mostly \'be patient\'

[michealv]

This is my video tutorial on orbital rendezvous - mostly \'be patient\'

Another great youtube video, awesome he does it pretty much exactly the same way as I did (except i didn\'t leave debris in space)

[Awaras]

This is my video tutorial on orbital rendezvous - mostly \'be patient\'

Yay!

My first sucessful rendezvous!

Thank you very much for your video guide.

[michealv]

Yay!

My first sucessful rendezvous!

Thank you very much for your video guide.

Its a great feeling of accomplishment isn\'t it!